The present invention relates to a process for the preparation of hydrazine hydrate. The present invention relates more specifically to an improved process for the manufacture of hydrazine hydrate from methyl ethyl ketone azine obtained by oxidation of ammonia with hydrogen peroxide in the presence of a coreactant or of a catalyst.
The industrial production of hydrazine hydrate is carried out according to the Raschig, Bayer or hydrogen peroxide processes.
In the Raschig process, ammonia is oxidized with a hypochlorite in order to obtain a dilute hydrazine hydrate solution, which solution subsequently has to be concentrated by distillation. This process is not very selective, has a low yield and is highly polluting, and is virtually no longer used.
The Bayer process is an alternative form of the Raschig process which consists in shifting a chemical equilibrium by trapping, using acetone, the hydrazine formed in the azine form (CH3) 2Cxe2x95x90Nxe2x80x94Nxe2x95x90Cxe2x80x94(CH3) 2. The azine is subsequently isolated and then hydrolysed to hydrazine hydrate. The yields are improved but there is no improvement with respect to the discharges to the environment.
The process with hydrogen peroxide consists in oxidizing a mixture of ammonia and a ketone with hydrogen peroxide in the presence of a means for activating the hydrogen peroxide in order to directly form the azine, which it is sufficient subsequently to hydrolyse to hydrazine hydrate. The yields are high and the process is not polluting. This process with hydrogen peroxide is used by the Applicant Company and is disclosed in numerous patents, for example U.S. Pat. No. 3,972,878, U.S. Pat. No. 3,972,876, U.S. Pat. No. 3,948,902 and U.S. Pat. No. 4,093,656.
The hydrolysis of an azine to hydrazine hydrate is disclosed in Patents U.S. Pat. No. 4,724,133 (Schirmann et al.), U.S. Pat. No. 4,725,421 (Schirmann et al.) and GB 1,164,460. This hydrolysis is carried out in a distillation column which is fed with water and azine. The ketone is recovered at the top and the hydrazine hydrate at the bottom.
EP 70,155 also discloses another hydrogen peroxide process.
These processes are also described in Ullmann""s Encylopedia of Industrial Chemistry (1989), vol. A 13, pages 182-183 and the references included.
In hydrogen peroxide processes, ammonia is oxidized with hydrogen peroxide in the presence of a ketone and of a means for activating the hydrogen peroxide according to the following overall reaction, an azine being formed: 
The activation means can be a nitrile, an amide, a carboxylic acid or a selenium, antimony or arsenic derivative. The azine is then hydrolysed to hydrazine and the regenerated ketone is recycled according to the following reaction: 
This hydrolysis is carried out in a distillation column. The ketone is recovered at the top and the hydrazine hydrate at the bottom. The Applicant Company has discovered that, in these hydrogen peroxide processes and using methyl ethyl ketone (MEK), small amounts of a by-product, MEK oxime 
were formed and that the presence of this oxime disrupted the operation of the process. In particular, the oxime is difficult to separate from the azine, it is found in the column for hydrolysis of the azine and it leads to decomposition of the hydrazine hydrate. The process of the invention consists in bleeding off this oxime.
The present invention is therefore a process for the preparation of hydrazine hydrate, in which:
(a) ammonia, hydrogen peroxide and methyl ethyl ketone are reacted in the presence of a working solution in order to form an azine;
(b) the working solution is separated from. the azine comprising methyl ethyl ketone oxime and optionally methyl ethyl ketone;
(c) the working solution is recycled to the stage (a) after an optional treatment;
(d) the azine is hydrolysed in order to obtain hydrazine hydrate and the methyl ethyl ketone is regenerated;
(e) the methyl ethyl ketone is recycled to the stage (a), this process being characterized in that, in the stage (d), methyl ethyl ketone oxime is bled off.
The hydrogen peroxide can be used in the usual commercial form, for example as an aqueous solution comprising between 30 and 90% by weight of H2O2. One or more conventional stabilizers for peroxide solutions can advantageously be added, for example phosphoric acid, pyrophosphoric acid, citric acid, nitrilotriacetic acid, ethylenediaminetetraacetic acid or the ammonium or alkali metal salts of these acids. The amount to be used is advantageously between 10 and 1000 ppm and preferably between 50 and 250 ppm of the combined reactants and working solution at the reactor inlet. The ammonia can be anhydrous or in aqueous solution
The working solution comprises a means for activating the hydrogen peroxide, that is to say a product such that the azine can be produced from ammonia, hydrogen peroxide and methyl ethyl ketone.
This activator can be chosen from organic or inorganic oxyacids, their ammonium salts and generally their derivatives: anhydrides, esters, amides, nitriles, acyl peroxides, or their mixtures. Use is advantageously made of amides, ammonium salts and nitrites.
Mention may be made, by way of examples, of (i) amides of carboxylic acids of formula R5OOH, in which R5 is hydrogen, a linear alkyl radical having from 1 to 20 carbon atoms, a branched or cyclic alkyl radical having from 3 to 12 carbon atoms or a phenyl radical which can be substituted, or (ii) amides of polycarboxylic acids of formula R6(COOH)n, in which R6 represents an alkylene radical having from 1 to 10 carbon atoms and n is an integer greater than or equal to 2, or R6 can be a single bond and then n has the value 2. The R5 and R6 radicals can be substituted by halogens or OH, NO2 or methoxy groups. Mention may also be made of the amides of the organic acids of arsenic. The organic acids of arsenic are, for example, methylarsonic acid, phenylarsonic acid and cacodylic acid.
The preferred amides are formamide, acetamide, monochloroacetamide and propionamide.
Use is advantageously made, among ammonium salts, of the salts of hydracids, of inorganic oxyacids, of arylsulphonic acids, of R5COOH acids or of R6(COOH)n acids, R5, R6 and n being defined above, or of the organic acids of arsenic.
The preferred ammonium salts are the formate, acetate, monochloroacetate, propionate, phenylarsonate and cacodylate. Mention may advantageously be made, among the nitriles, of the products of formula R7(CN)n, it being possible for n to vary from 1 to 5, depending on the valency of R7, and R7 being a cyclic or non-cyclic alkyl having from 1 to 12 carbon atoms or benzene or pyridine. R7 can be substituted by groups which are not oxidized in the reactor of the stage a, for example halogens or carboxyl, carboxylic ester, nitro, amine, hydroxyl or sulphonic acid groups.
The preferred nitriles are acetonitrile and propionitrile.
The working solution is formed by dissolving one or more products chosen from organic or inorganic oxyacids, their ammonium salts and generally their derivatives: anhydrides, esters, amides, nitriles, acyl peroxides, or their mixtures. Use is advantageously made of the preceding amides, ammonium salts or nitriles.
This solution can be aqueous or based on an alcohol or on a mixture of alcohol and water. Use is advantageously made, among the alcohols, of saturated aliphatic alcohols having from 1 to 6 carbon atoms and preferably 1 or 2 carbon atoms.
Use is also advantageously made of diols and more particularly of diols having from 2 to 5 carbon atoms. Mention may be made, for example, of glycol, propylene glycol, 1,3-propanediol, 1,3- and 1,4-butane-diol and 1,5-pentanediol.
According to an advantageous form of the invention, the working solution is an alcoholic solution of an organic acid of arsenic and is disclosed in Patent EP 70,155, the contents of which are incorporated in the present application. According to another advantageous form of the invention, the working solution is an aqueous solution of an amide of a weak acid and of the ammonium salt corresponding to this acid, such as disclosed in Patent EP 487,160.
These amides of weak acids are derived from the corresponding carboxylic acids which have a dissociation constant of less than 5xc3x9710xe2x88x925, that is to say acids which have a pK of greater than 4.3 in aqueous solution at 25xc2x0 C.
For the polycarboxylic acids, these are the acids for which the constant of the first ionization is less than 5xc3x9710xe2x88x925.
Mention may be made, by way of examples, of the carboxylic acids of formula R8COOH, in which R8 is a linear alkyl radical having from 1 to 20 carbon atoms or a branched or cyclic alkyl radical having from 3 to 12 carbon atoms or a phenyl radical which can be substituted, or of polycarboxylic acids of formula R9(COOH)n, in which R9 represents an alkylene radical having from 1 to 10 carbon atoms and n is a number greater than or equal to 2, or R9 can be a single bond and then n has the value 2. The R8 and R9 radicals can be substituted by halogens or OH, NO2 or methoxy groups. Use is preferably made of acetamide, propionamide, n-butyramide or isobutyramide.
The ammonium salt corresponding to acetamide is ammonium acetate.
It would not be departing from the scope of the invention to form the ammonium salt in situ, that is to say to use the corresponding carboxylic acid which gives the ammonium salt by reaction with ammonia.
The proportions of the amide and of the corresponding ammonium salt can vary within wide limits. Use is usually made of 1 to 25 parts of the ammonium salt per 5 parts of amide and preferably 2 to 10.
The reactants can be used in stoichiometric amounts. However, use is made, per mole of hydrogen peroxide, of 0.2 to 5 mol and preferably of 1.5 to 4 mol of methyl ethyl ketone and of 0.1 to 10 mol and preferably of 1.5 to 4 mol of ammonia. The amount of working solution is between 0.1 and 1 kg per mole of hydrogen peroxide. This amount depends on its quality, that is to say on its catalytic strength or its activity which makes it possible to convert the reactants to azine. The proportions of the reactants laid down above make it possible to obtain complete conversion of the hydrogen peroxide and a production of azine corresponding to more than 50%, and which can reach 90%, of the hydrogen peroxide charged.
The hydrogen peroxide, ammonia and methyl ethyl ketone can be brought into contact with the working solution in any way.
The reaction is advantageously carried out in a homogeneous medium or in a medium which provides at least sufficient solubilization of the reactants for it to be possible to obtain the azine. The reaction can be carried out in a very wide temperature range, for example between 0 and 100xc2x0 C., and is advantageously carried out between 30 and 70xc2x0 C. Although it is possible to carry out the reaction at any pressure, it is simpler to be at atmospheric pressure. However, the pressure can rise up to approximately 10 bar if this is necessary in order to preferably maintain the reaction of the stage a in the liquid phase.
The reactants can be introduced simultaneously or separately and in any order into the working solution. It is possible to use all kinds of reactors, stirred or nonstirred, or even simple tanks, which can be arranged in parallel or in series, cocurrentwise or countercurrentwise, or any combination of these possibilities.
Known means, such as liquid-liquid extraction, distillation, separation by settling or any combination of these possibilities, are used to separate (i) the azine and optionally the excess methyl ethyl ketone and (ii) the working solution.
Methyl ethyl ketone is advantageous because its azine is insoluble in the working solution.
The working solution can be treated in the stage (c).
The stages (a), (b) and (c) are disclosed, for example, in Patents EP 399,866 and EP 518,728, the contents of which are incorporated in the present application.
The Applicant Company has observed, for example, that the azine obtained in the stage (b), after separation from the working solution, is accompanied by unreacted methyl ethyl ketone and by various impurities. The Applicant Company, without being bound by this explanation, believes that these impurities are formed during the stage (a) and are due to the simultaneous presence of hydrogen peroxide, ammonia, methyl ethyl ketone and the agent for activating H2O2. These impurities include methyl ethyl ketone oxime 
which is difficult to separate by distillation from the azine major product, with the result that, in industrial processes, they are conveyed simultaneously into the equipment which makes possible hydrolysis of the azine to hydrazine hydrate. Doing which, the Applicant Company has discovered that, when this hydrolysis is carried out in a reactive plate column, the oxime is concentrated on certain plates but an abnormal decomposition of the hydrazine hydrate is also observed, resulting in significant falls in yield.
The object of the present invention is to provide a means for not suffering from losses in yield by simply drawing off the oxime steadily via a side-stream, so as to prevent it from accumulating. Doing which, it is actually observed that the yield of hydrolysis of the azine to hydrogen hydrate remains high and does not decrease.
The stage (d) is carried out, for example, in a plate or packed column of distillation column type which is fed with the azine originating from the stage (b) and water. The following are obtained: (i) at the top, methyl ethyl ketone in the form of an azeotrope with water, and (ii) at the bottom, an aqueous hydrazine hydrate solution.
The hydrolysis of azines is known. For example, E. C. Gilbert, in an article in the Journal of the American Chemical Society, vol. 51, pages 3397-3409 (1929), describes equilibrium reactions for the formation of azine and the hydrolysis reactions of the latter and provides the thermodynamic parameters of the system in the case of water-soluble azines. For example, the hydrolysis of acetone azine is disclosed in U.S. Pat. No. 4,724,133. As regards azines which are. insoluble in aqueous solutions (for example, methyl ethyl ketone azine 
the hydrolysis has to be carried out in a reactive column, such that, by continuously separating the methyl ethyl ketone at the distillation column top and the hydrazine hydrate at the column bottom, complete hydrolysis can be achieved. Of course, this system works best when the operation is carried out continuously, as disclosed in French Patent 1,315,348, British Patent 1,211,547 or Patent U.S. Pat. No. 4,725,421.
In all these patents, the reaction is carried out in a packed distillation column or better. still a plate distillation column operating under a pressure of 2 to 25 bar with a bottom temperature of 150xc2x0 C. to 200xc2x0 C.
When the operation is carried out with pure azine, that is to say obtained from hydrazine hydrate and methyl ethyl ketone, for example, it is actually found, by operating according to these patents, that dilute hydrazine hydrate solutions are obtained with a good yield.
In this column, the azine is hydrolysed and the hydrazine hydrate is separated from the methyl ethyl ketone. These conditions are known. A person skilled in the art easily determines the number of plates or the packing height, as well as the points for feeding with azine and with water. Solutions comprising 30 or even up to 45% by weight of hydrazine hydrate are obtained at the bottom. This molar ratio of water to azine in feeding this column is at least greater than stoichiometry and advantageously between 5 and 8. The column bottom is between 150xc2x0 C. and 200xc2x0 C., preferably 175 to 190xc2x0 C. The pressure depends on the boiling temperature of the azine, water and the reactant carrying a carbonyl group. Such a hydrolysis is disclosed in U.S. Pat. No. 4,725,721.
A person skilled in the art can easily determine, according to the number of plates or the packing height, the position of the azine feed and the position of the water feed, the reflux, the nature of the azine, and the like, in what part of the column the maximum oxime concentration is obtained. This is because it is simpler to bleed off the oxime by drawing off at the point of its maximum concentration. Drawing off can be carried out continuously or batchwise, the essential point being to avoid the accumulation of oxime in this column since its presence results in decomposition of the hydrazine hydrate.
The reaction of the stage (a) can produce an azine comprising up to 2% by weight of oxime.
The concentration of oxime is prevented from exceeding 15% by weight on the plates or in the parts of the column of its maximum concentration.
For example, when the operation is carried out with methyl ethyl ketone azine resulting from an oxidation operation with hydrogen peroxide according to Patent EP 70,155 or according to Patents EP 399,866, EP 518,728 or EP 487,160, it is observed that this azine is not pure but that it comprises an amount of oxime which can vary between 0.1 and 1% of methyl ethyl ketone oxime 
the boiling point of which is 151xc2x0 C. at atmospheric pressure, in comparison with 161xc2x0 C. for methyl ethyl ketone azine. It is illusory to want to separate these two compounds by distillation. By means of recycling operations, the level of oxime can even rise to several percent.
The Applicant Company has found that, industrially, the azine comprising the oxime could be introduced into the hydrolysis column and that this oxime, because of its azeotropic behaviour with water, came to be distributed in the column at a level intermediate between the hydrazine hydrate and the methyl ethyl ketone and that, for this reason, it was possible, fairly easily, to separate it via a side-stream. This being the case, the Applicant Company has also found that, if the level of oxime is allowed to rise in the column, an increasing degree of decomposition of the hydrazine hydrate is concurrently observed. This decomposition is related to the presence of oxime, as is shown in the examples.